An electronic key system is known as a system for performing operations in a vehicle without using a mechanical key. The electronic key system is provided with a keyless entry function for unlocking doors when a user (driver) holding an electronic key approaches a door and locking the doors when the user moves away from a door. The electronic key system is also provided with an ignition function for starting the engine by just rotating an ignition switch without inserting a mechanical key into a key cylinder.
The electronic key system includes an electric steering lock, which electrically locks and unlocks a steering wheel. The electric steering lock has a lock bar that is moved by a lock motor. The lock bar is engaged with a socket formed in the steering shaft to lock the steering shaft. The steering shaft is unlocked when the lock bar is removed from the socket of the steering shaft.
The electric steering lock includes a lock switch and an unlock switch. The lock switch goes ON when the steering shaft is locked to output an H level signal (lock signal). The unlock switch goes ON when the steering shaft is unlocked to output an H level signal (unlock signal). The electric steering lock determines whether the steering shaft is locked or unlocked based on the output signal from the lock switch or the unlock switch. An electric non-contact switch having high durability and reliability is used as the lock and unlock switches. An example of such an electric non-contact switch is a Hall IC.
The operation of the electronic key system when starting the engine will now be described. When the steering shaft shifts to the unlock state from the lock state, the unlock switch is switched ON to generate an unlock signal. The electric steering lock provides the unlock signal to an engine ECU. When receiving the unlock signal, the engine ECU starts the engine if the electronic key and the vehicle achieve ID code authentication and the ignition switch is rotated to the engine start position.
When operation voltage decreases, the voltage of a detection signal of the electric non-contact switch may decrease. For example, when starting (cranking) the engine, the starter motor and igniters consume much battery voltage. Thus, the unlock switch may not be supplied with sufficient voltage. This would decrease the voltage of the output signal from the unlock switch. Particularly, decrease in the operation voltage of the unlock switch tends to occur when the battery has deteriorated or when cranking is performed at low temperatures.
When the unlock switch is in a low voltage state, the output of an H level signal, or an unlock signal, may not be maintained. In such a case, no unlock signal will be provided from the electric steering lock to the engine ECU even though the steering shaft is in the unlock state. Since the unlock signal is necessary to start the engine, the engine ECU will not start the engine. Therefore, the electronic key system of the prior art using such an electric steering lock may erroneously determine that the steering shaft is in the unlock state when the operation voltage decreases. It is thus required that such an erroneous determination of the steering shaft being in the unlock state be prevented even when the battery voltage is low.